The invention relates to a spool valve comprising a valve housing, in the interior of which an axially extending spool receiving space is provided, in which a valve spool is arranged, the valve housing being longitudinally divided in the area of the spool receiving space with the formation of a plurality of longitudinally extending housing parts, and a plurality of sealing rings which are in direct sealing contact with the valve spool so as to define flow paths and which are arranged coaxially in relation to the valve spool in an axial sequence with a spacing in relation to one another.
Such a valve is known, see the European patent publication 0 122 247 B1. It has a valve housing in whose interior space a sleeve is arranged, which functions as a spool receiving space and receives valve spool for longitudinal sliding motion. For the insertion or the sleeve and of the valve spool the valve housing is longitudinally divided into two halves for the extent of the spool receiving space. The sleeve has peripheral holes via which the valve ducts are in communication with the spool receiving space so that different flow paths may be predetermined for the fluid in the valve in a manner dependent on the setting of the spool. In order to prevent the fluid from flowing in an uncontrolled manner between the sleeve and the valve spool in the longitudinal direction, the valve spool has a plurality of annular seals, which are able to slide on the inner periphery or bore of the sleeve while in tight sealing engagement therewith.
Because the spool receiving space is defined by the sleeve there is the advantage of a satisfactory guiding action and the possibility of the arrangement and formation of choke openings which under operational conditions are to prevent sharp pressure surges, but there is the disadvantage that there has to be a static seal between the valve housing and the sleeve in order to prevent longitudinal flow of fluid in the part radially extending between the housing parts and the sleeve. The sealing action is produced by means of sealing rings, which are seated in grooves in the housing parts and coaxially surround the sleeve at a plurality of positions. The assembly and insertion of the sleeve is relatively complex, since it has to be fitted with the sealing rings prior to placing it in the housing halves, this being particularly difficult if such rings are, as is provided for, designed with a housing seal operating between the housing parts. In addition to the extra design complexity owing to the sleeve there is furthermore an increase in the danger of possible leaks, since the radial sealing action which is necessary both internally and externally, calls for a substantial number of sealing joints. Moreover the sealing rings necessary for predetermining the flow paths and in direct sealing contact with the valve spool are snapped into grooves in the valve spool with the result that during the assembly thereof they can be subject to damage to the extent that they may be overstretched on slipping them on the valve spool or because they have to be slid over preceding receiving grooves prior to reaching the groove inside the spool for which they are in fact intended and during such sliding motion have to be dragged over sharp groove edges.
In order to deal with such problems as described there has already been a proposal in the German patent publication 4,027,520 C2 to design the sealing rings in the form of cartridge-like units, which are separately inserted into the spool receiving space of a valve housing which is shut off peripherally. However this calls for relatively complex positioning measures and extremely accurate matching between relationships between the tolerances of the part. A further known alternative possibility provided in the German patent publication 3,641,383 A1 is to have a peripherally closed valve housing with transverse slots, into which the sealing rings are inserted so that they assume positions in the spool receiving space where they can cooperate with the spool valve which in this case has no seals. The openings of the insertion slots are covered over by means of a cover plate which is mounted on the outside of the valve housing. On insertion of the spool valve it is possible the sealing rings to be damaged, since are not accessible at all. Furthermore as in this case of the said German patent publication 4,027,520 C2 there is no possibility, in the case of a valve with small overall dimensions, to check the workmanship of the spool receiving space.